Venous blood has long been collected for various medical tests. Recently, it has become more important to also collect arterial blood for measuring of the partial pressures of dissolved oxygen and carbon dioxide in the arterial system.
When collecting a blood sample, it is important to distinguish at the time of collection whether it is arterial or venous blood. In the past, arterial blood has been detected by use of glass syringes in which the arterial blood pressure would be sufficient to force back the syringe plunger; venous pressure would not. U.S. Pat. No. 3,930,429 also proposes a plastic syringe system for distinguishing arterial pressure. However with plunger type arterial blood collectors, these plungers can sometimes catch and drag, making it difficult to clearly distinguish that the blood is arterial.
Recently, others have proposed the use of a glass tube connected to a needle, thereby eliminating the plunger. Such device required the use of a manually applied cork to plug the rear end of the glass tube to prevent the blood sample from spilling out. Because the glass tube was rigid, it was also difficult to dispense the blood sample into a machine that did not have a vacuum extractor for the blood sample. Because it did not have a plunger, such sample could not be forced into the machine.
Additional problems with prior arterial blood samplers have included transmission of oxygen through the sampler's wall to cause erroneous readings on the blood, and liquid heparin in the sampler which introduced an error into the readings for oxygen and carbon dioxide. These problems are described in the following publications:
Scott et al., "Leakage of Oxygen From Blood and Water Samples Stored in Plastic and Glass Syringes," British Medical Journal, Aug. 28, 1971, 3, pp. 512-516. PA1 Hansen et al., "A Systematic Error in the Determination of Blood Pco.sub.2," American Review of Respiratory Disease, Vol. 115, 1977, pp. 1061-1063. PA1 Hamilton et al., "Arterial Blood Gas Analysis: Potential Errors Due to Addition of Heparin," Anaesthesia and Intensive Care, Vol. VI, No. 3, August 1978, pp. 251-255.